The effects of adaptive pressure ventilation–synchronised intermittent mandatory ventilation and pressure-controlled synchronised intermittent mandatory ventilation on pulmonary mechanics and arterial gas analyses during laparoscopic cholecystectomy

Background

Hypercapnia and elevated intraabdominal pressure from carbon dioxide (CO₂) pneumoperitoneum can adversely affect respiratory mechanics and arterial blood gases. We tested the hypothesis that adaptive pressure ventilation–synchronised intermittent mandatory ventilation (APV-SIMV) may provide better pulmonary mechanics, CO₂ homeostasis and pulmonary gas exchanges with less frequent ventilatory settings (tidal volume (TV), respiratory rate (RR)) and lower peak inspiratory pressure (P_peak) and plateau pressure (P_plat) than pressure-controlled synchronised intermittent mandatory ventilation (P-SIMV) in patients undergoing laparocopic cholecystectomy (LP).

Method

The study group consisted of 40 patients (APV-SIMV n = 20, P-SIMV n = 20). LP was performed under total intravenous anesthesia. After induction of anesthesia, a RR of 12 breaths/minute, and an inspiratory:expiratory rate of 1:2 and PEEP of 6 cmH₂O were set for both groups. APV-SIMV was started with a target TV of 8 ml/kg. P-SIMV was started with the inspiratory pressure (P_ins) that will provide 8 ml/kg TV. The settings were changed until target parameters to maintain normocapnia and normoxia were achieved (ETCO₂ 30–35 mmHg, PaCO₂ 35–45 mmHg and SaO₂ >90%). When the target parameters could not be achieved, the first RR was increased by 2 breaths/minute up to 16 breaths/minute, then the volume or pressure was titrated to induce 1 ml/kg increases in TV up to 10 ml/kg. The initial FiO₂ was set to 50%. FiO₂ was increased with increments when the SaO₂ fell below 90%. PaO₂/FiO₂, static compliance, VD/VT, P_peak and P_plat, ETCO₂, inspiratory and expiratory resistances, and arterial blood gas analysis were recorded before, during and after pneumoperitoneum. Statistical analysis were carried out using the chi-square test, paired test and independent samples test when appropriate.

Results

Demographic data were similar between groups. Pneumoperitoneum caused significant decreases in static compliance and arterial pH, and increases in P_peak and P_plat, VD/VT and ETCO₂ in both groups. However, APV-SIMV resulted in fewer setting changes, lower peak and plateau pressures, VD/VT, and ETCO₂ levels when compared with P-SIMV (P < 0.025).

Conclusion

APV-SIMV may provide better results then conventional P-SIMV in patients undergoing LP.